Diatom species composition in the in situ diet of the placer oyster Crassostrea corteziensis in an estuarine system

Abstract

Background: The feeding of cultured mollusks has been based on a few strains of diatoms and green algae; however, it has been shown that these have low nutritional value. Therefore, alternatives have been searched as in this case by resorting to the study of in situ feeding of these mollusks. Goals: To elaborate a floristic list of diatoms that are part of the in-situ diet of Crassostrea corteziensis, both wild and in extensive culture at the aestuarine wetlands of Nayarit, Mexico. Methods: A total of 130 oysters were sampled from three sites and three distinct substrates, i.e., string, sediment, and mangrove roots of the estuarine system, during November 2013, and March and June 2014. Their digestive systems were dissected and their gut contents examined, oxydized and mounted in synthetic resin for the identification of the diatoms ingested in-situ. Results: We identified 212 species and varieties of diatoms. Benthic forms composed 72.6% of the species richness, out of which 50% are of marine affinity, 16% are freshwater forms, and 14% were brackish water forms. The size of pennate diatoms varied between 7.4-230 μm long and 2.82-50.61 μm wide; while the diameter of centric diatoms varied between 4.89-123 μm. Conclusions: The in-situ diet of C. corteziensis showed a high species richness and a benthic origin. The species richness and composition of diatoms in the gut contents of C. corteziensis is characteristic of estuarine sediments and represents an approximate description of the benthic diatom taxocenosis of estero Camichin, Nayarit and similar environments in the region. According to their frecuency, taxa such as Cyclotella striata, Cymatotheca weissflogii, Neodelphineis silenda, Shionodiscus oestrupii and Thalassionema nitzschioides var. capitulatum represent alternatives for the in vitro culture of placer oyster.